1. Field of the Invention
This invention relates to an image forming apparatus such as a printer or a copying machine, and particularly to an image forming apparatus provided with a scanning unit emitting a laser beam.
2. Description of Related Art
FIG. 4 of the accompanying drawings shows an image forming apparatus according to the prior art. In a housing 101, there is contained an optical scanning device 102. The optical scanning device 102 is contained in the housing 101 while an openable and closable member 104 which is a portion of the housing 101 remains opened, and is positioned and fixed at a predetermined position.
That is, the openable and closable member 104 located on the upper surface of the housing 101 is opened, and the optical scanning device 102 is inserted from above. The optical scanning device 102, as shown in FIG. 5 of the accompanying drawings, is installed at a predetermined position in the housing 101 relative to a photosensitive drum 103. The optical scanning device 102 is fixed at four locations by screws 105 in a state in which the openable and closable member of the housing 101 is opened, and the work of fixing the optical scanning device 102 is terminated.
After the work of fixating the optical scanning device 102 has been terminated, an opening portion 101A is closed by the openable and closable member 104 in the upper portion, and the housing 101 is completed so as to surround the optical scanning device 102 in the housing 101 in the shape of a box. Thereby, the housing has housing strength which can withstand a load during the operation, the insertion shock of a cartridge (CRG) and a shock during shipment.
However, in an image forming apparatus provided with the photosensitive drum 103 and the optical scanning device 102, it is necessary to dispose the locations of both of them accurately in the interior of the housing 101. Moreover, the optical scanning device 102 must be housed and disposed in the interior of the housing 101 and therefore, the opening portion 101A to a housing portion in the housing 101 must be provided without fail. Consequently, when the opening portion 101A is provided and the optical scanning device 102 is to be housed in the housing 101, a portion of the housing 101 is opened in the opening portion 101A and therefore, the strength of the housing 101 is more reduced than in a state in which the opening portion 101A is closed by the openable and closable member 104.
Accordingly, even if the optical scanning device 102 is housed accurately relative to the photosensitive drum 3 with the openable and closable member 104 being opened, the strength of the housing 101 is reduced and therefore, during the time until the opening portion 101A is closed by the openable and closable member 104 and the strength of the housing 101 is completed, distortion occurs to the housing 101 and after all, there has been the possibility that disorder occurs to the positions of the photosensitive drum 103 and the optical scanning device 102.
Particularly, in the case of an image forming apparatus housing a plurality of optical scanning devices 102 therein, the rate of a housing portion housing the optical scanning devices 102 occupied in the housing 101 becomes great and moreover, the opening portion 101A for inserting the optical scanning devices 102 therethrough into the housing portion also becomes large and therefore, the possibility that disorder occurs to the positions of the photosensitive drum 103 and the optical scanning devices 102 before the strength of the housing 102 is completed has become high.
Also, to obtain the strength of the housing with the openable and closable member 104 opened, it is necessary to increase the skeletal parts of the housing for reinforcement or to make the skeletal parts of the housing high in strength, and this has compelled a considerable increase in cost.
Further, when in the market, some trouble occurs to the optical scanning devices 102 and the interchange thereof becomes unavoidable, it is also necessary to open the opening portion 101A of the housing 101. If at such time, the loading portion of the housing 101 is opened in a place where, unlike a production site, there is no jig for accurately supporting the housing, distortion may occur to the housing 101 depending on the unevenness of a floor on which the image forming apparatus is installed. Accordingly, when the positions of the optical scanning devices 102 are determined with the opening portion opened, there has been a case where after all, disorder occurs to the positional relation between the photosensitive drum 103 and the optical scanning device 102 after the openable and closable member is closed. As described above, there has been a case where not only the relative position of the optical scanning device to the photosensitive drum, but also when there are a plurality of optical scanning devices, the relative position between the optical scanning devices is not ensured.
It is an object of the present invention to provide an image forming apparatus which enables a scanning unit to be accurately positioned in the main body thereof.
It is another object of the present invention to provide an image forming apparatus having a scanning unit emitting a laser beam, and an openable and closable member openable and closable relative to an image forming apparatus main body, the openable and closable member having a positioning portion for positioning the scanning unit.
Further, objects of the present invention will become apparent from the following description.